Growth hormone (GH) messenger RNA (mRNA) will be identified in and isolated from a line of rat pituitary tumor cells (GC). A cell-free system derived from wheat germ has been developed for the translation of GH mRNA, and will be used as an assay system to monitor the purification of GH mRNA. Characterization of the product of translation of GH mRNA in this system is under way, and will be continued. When a purified hypothalamic GH release factor is available, its effects on intracellular GH mRNA levels will be studied. When highly purified GH mRNA has been prepared, it will be used as a template for the synthesis of radioactive complementary DNA (cDNA). This cDNA will be used as a probe for studies of intranuclear GH mRNA and GH DNA.